Star polymers are well known and have been used in coating compositions as dispersing agents, rheology control additives, adhesion promoters and the like and in plastics as impact modifiers, reinforcing additives, stiffening modifiers and the like. Star polymers are shown in Spinelli U.S. Pat. No. 4,659,783 issued Apr. 21, 1987. Star polymers made via group transfer polymerization are shown for example in Spinelli U.S. Pat. No. 4,695,607 issued Sep. 22, 1987. Dense star polymers are shown in Tomalia et al U.S. Pat. No. 4,568,737 issued Feb. 4, 1968. Star polymers have been prepared by anionic copolymerization as shown in Journal of Polymers Science, part C Polymer Symposia, No. 22, 145-156 (1968).
Making star polymers by via group transfer polymerization is relatively expensive and difficult. Also, the choice of monomers that can be used is limited, e.g., hydroxy or silane functional monomers can not be used directly but require the use of intermediates to block the functionality of the monomers. Conventional anionic polymerization is not difficult and is relatively inexpensive in comparison to group transfer polymerization but also has a limitation on the monomers that can be used and does not produce uniform star polymers but results in forming unwanted polymeric components with the star polymer. There is a need for an improved process for making star polymers and in particular dispersions of star polymers in which the polymer contains desired functional groups that are useful in coating compositions and plastics and that are easily made and at a relatively low cost.